Sputtering is a known means for depositing thin films onto a substrate, such as those especially useful in the manufacture of semi-conductor devices, including integrated circuits. In such known sputtering systems, the material that is deposited onto a substrate is removed from a sputter target by bombarding the target with ions. However, the process imparts thermal energy to the target. In order to prevent the target from overheating, the target is often mounted to a backing plate to dissipate heat. Thus, it is important that a good thermal bond is present between the target and the backing plate.
Since the target and backing plate are often formed from different materials, they often have different rates of thermal expansion, resulting in the target potentially bowing or otherwise becoming dimensionally unstable upon cooling. As a result, such assemblies must undergo a time-consuming flattening and reshaping procedure to orient the target assembly into its desired, planar orientation. Unfortunately, such flattening procedures often introduce torsional, or other stresses on the assembly areas, including the bonding layer between the target and the backing plate, often leading to assembly failure.
Known methods for diffusion-bonding in the manufacture of sputter target assemblies use hot iso-static press (HIP) methods to bond solid target blanks to backing plates with or without bond media. The bond media can be metal foils or interlayer coated on the target or backing plate bond surface by plating, sputtering or other coating techniques.
U.S. Pat. No. 5,397,050 provides a method to use HIP processing to consolidate a W—Ti powder to form a target while bonding the powder composition to the titanium backing plate to form an inter-diffusion type bond between the target and the backing plate. In this art, the powder and the backing plate are placed in a metal can. By applying HIP, the powder is compacted and inter-diffused to the backing plate. After HIP, the assembly is flattened in a separate flattening step by a platen press prior to machining.
U.S. Pat. No. 5,836,506 describes the bonding of a target to a backing plate by controlling the roughness of bond surface between 120 Ra to 150 Ra, and drilling a plurality of holes in one of the bond surfaces. A pressure of 30 MPa (4.35 ksi) to 140 MPa (20 ksi) and 450° C. to 550° C. is applied for targets bonded to Al or Al alloy backing plates, 742° C. to 947° C. for targets bond to Cu or Cu alloy backing plates, 982° C. to 1232° C. for targets bond to steel backing plates or 1182° C. to 1472° C. for targets bond to Ti or Ti alloy backing plates.
U.S. Pat. No. 5,230,459 describes a method for forming a target to a backing plate with a plurality of grooves in one of the bond side by machining, normally the grooves are on the target side. The assembly is heated and pressed under vacuum, inert or reduction environment. When bonding a Ti target to an Al backing plate, bonding is taught as occurring at 550° C. to 625° C. and under 2 ksi to 15 ksi by HIP. For bonding target to Cu backing plate, the bond temperature is taught as being less than the melting point of Cu or Cu alloys.
U.S. Pat. No. 6,749,103 provides a method for bonding a target to a backing plate followed by an annealing at a temperature of from 200° C. to 482° C. A plurality of salient portions, M-shaped ridges or projections are machined into a bond surface, depending on whether the target or backing plate is the harder surface. The projection from the harder metal penetrates into the softer metal by cold pressing at pressures of about 50 tons to 5000 tons. After the low temperature pressure consolidation, the assembly is subjected to 200° C. to 482° C. to ensure adequate adhesion of the pressure consolidated surfaces.
U.S. Pat. No. 5,693,203 describes a bonding method for a target to a backing plate using at least one insert as the bond medium. The insert is made of a soft material such as Al and Al alloys, Cu and Cu alloys, Ag and Ag alloys, or Ni and Ni alloys. The insert thickness is 10 μm or thicker, and can be foil or a sheet and coating film provided by plating, vapor deposition, or sputtering. The target, backing plate and insert are degreased and rinsed with an organic solvent like acetone. The bonding is performed at temperatures of 150° C. to 350° C. and pressure at 1.0-15 kg/mm2 (1.42-21.3 ksi), preferably of 150° C.-250° C. and 3-10 kg/mm2 (4.26-14.2 ksi). The insert is applied when using Al and Al alloys, Cu and Cu alloys, and stainless steels as the backing plates. The targets are bonded at a temperature of 150° C.-550° C. with 1 kg/mm2 minimum. The examples presented disclose that pressure of 7.5 kg/mm2-8 kg/mm2 (10.65-11.36 ksi) is applied for W target and Ti target bonded with Ti backing plate at 500° C.
U.S. Pat. No. 6,071,389 describes a method of diffusion bonding a cobalt target to an aluminum or copper backing plate by means of a titanium interlayer. The Ti interlayer is provided as a foil, but may be also be formed on a mating surface of either the target or the backing plate by electroplating, sputtering, electro-less plating, or plasma spraying. The target may be machined with grooves defining salient points prior to providing the interlayer. The bonding is performed at 600° C. with 100 MPa (14.5 ksi) pressure for three hours. The assembly may be made via vacuum-hot-press, but preferably by hot-isostatic-pressing.